1. Field of the Invention
The present invention relates to fuel nozzles for gas turbine combustors and more specifically to fuel nozzles that utilize multiple fuel types and have the capability for steam injection to control emissions of oxides of nitrogen (NOx).
2. Description of Related Art
Land based gas turbine engines typically include at least one combustor for producing hot gases necessary to drive the turbine section of the engine. Each combustor contains at least one fuel nozzle for injecting fuel to mix with compressed air from the engine compressor and react to form the hot gases. Depending on engine operating requirements and environmental issues, the fuel nozzles can inject multiple fuel types, including gaseous fuel and liquid fuel. In recent years, reductions in emissions levels, especially with respect to NOx and carbon monoxide (CO), have been the main focus of equipment manufacturers, especially since the operation of these types of engines are regulated primarily by their emissions output.
A well-known means to minimize NOx formation in a combustor having a dual fuel nozzle involves injecting steam, from the fuel nozzle, into the combustion chamber. NOx formation in a combustor is a function of flame temperature, where higher flame temperatures create higher levels of NOx emissions. Steam injection reduces the overall flame temperature, thereby creating lower NOx levels. However, if the steam is not injected with a high enough pressure drop across the steam circuit or at too high of a velocity, flow mal-distributions can occur where some regions of a combustion system receive excessive amounts of steam and other areas not receiving enough steam, thereby resulting in high combustion dynamics. High levels of combustion dynamics have been known to significantly reduce hardware life.
Therefore, what is needed is a fuel nozzle capable of injecting liquid fuel, gaseous fuel, or both simultaneously, along with steam, where the flow of steam through the nozzle to the combustor is regulated to reduce undesirable combustion dynamics.